1. Field of the Invention
The present invention relates to a dishwasher and more particularly, to a system for sensing light soil loads to allow an accurate cycle response thus improving washability and energy efficiency.
2. Description of Related Art
Domestic dishwashers in use today draw wash liquid from a sump at the bottom of a wash tub and spray the wash liquid within the wash tub to remove soils from dishes located on racks in the tub. It is well known that the removal of soils from the recirculating wash liquid positively impacts the wash performance of the dishwasher. Accordingly, to improve performance and efficiency, some dishwashers employ a system for separating soils out of the recirculating wash liquid wherein the soils are retained in a soil collector. Frequently, a filter screen is used to retain soil in the soil collector. For example, in U.S. Pat. No. 5,165,433, a dishwasher system is disclosed that includes a centrifugal soil separator which sends soil laden wash liquid into a soil container then wash liquid passes through a fine filter disposed in the wall of the soil container while soils are retained by the screen. Typically, backwash jets are directed against the filter by the lower wash arm in an attempt to clear the filter and prevent clogging.
U.S. Pat. No. 4,559,959 discloses a dishwasher wherein soil load is measured by monitoring pressure in a soil collector in which soils are retained after the wash liquid passes through a filter mesh. If the pressure exceeds a predetermined limit, indicating that the filter mesh is clogged, the wash liquid is completely purged by draining all of the wash liquid out of the tub and refilling the tub with fresh water. However, this dishwasher uses excess water and concerns over energy consumption have led to dishwashers utilizing purge systems that only partially drain the dishwasher tub. For example, U.S. Pat. No. 4,346,723 discloses a dishwashing system wherein soils are collected in a bypass soil collector and the soil collector may be purged by draining small amounts of wash liquid in spurts during an early wash period by selectively opening and closing a drain valve.
Since wash performance is effected by the soiled condition of the wash liquid recirculated through the system, all or a portion of the wash liquid may be drained from the dishwasher chamber if it is sensed that the soil collector has reached a predetermined pressure as disclosed in U.S. Pat. No. 5,900,070 and clean water can be introduced into the chamber. However, since the soil collector is usually provided with a screen that is backwashed, pressure only builds when there is a heavy soil load in the collector.
Wash performance in a dishwasher is also related to the temperature of the wash liquid. It is known that hot water is more effective for washing than cold water, particularly for oily soils, which melt at higher wash liquid temperatures. Accordingly, dishwashers are commonly connected to a hot water supply such that the fill water supplied into the dishwasher has a relatively high temperature. Thermal inputs during the dishwasher cycle typically occur during a thermal hold wherein the cycle of operation is interrupted while a heater is energized until a thermostat is satisfied or a maximum default time limit elapses. A dishwasher may have a pressure sensor for sensing fluid pressure within the soil collector such as is shown in U.S. Pat. No. 5,900,070. A control means energizes a heater disposed in a sump region of the wash chamber when the pressure within the soil collector exceeds a predetermined limit pressure. Heat energy is then supplied to the wash liquid in response to the soil load.
Detergents and wetting agents can affect the wash performance in a dishwasher. Chemical energy can affect the breakdown of soils and thus the ability of the wash liquid to remove soils from dishes. It is well known that the use of detergents and wetting agents positively impacts wash performance, so varying amounts of detergents and wetting agents would be useful for varying soil loads. It would be beneficial if the amount of detergent and/or wetting agent added to the wash liquid was responsive to the soiled condition of the wash liquid.
Unfortunately, there is currently no means of measuring light soil loads. Pressure in the soil collector usually indicates the presence of heavy soil loads because the backwash provided by the lower wash arm keeps light soil loads from clogging the filter and thus, from increasing pressure in the collection chamber.
Accordingly, it would be an improvement in the art if a dishwasher wash system was provided which could sense light soil loads in the dishwasher so a response could be initiated, for example, the addition of heat to the water, the addition of time to the cycle, the draining of soiled wash liquid or the addition of detergent.
The present invention is directed to an automatic dishwasher wash system that is responsive to the presence of light or oily soil loads. It is an object of the invention to provide a dishwasher having an interior wash chamber for receiving wash liquid and a sump region disposed at the bottom of the wash chamber. A wash pump is disposed in the sump region and has an intake through which wash liquid is drawn from the sump. The wash pump has a main outlet and a secondary outlet. The dishwasher draws wash liquid through the sump region into the wash pump intake and selectively directs wash liquid from the wash pump main outlet to the wash arm. Wash liquid is directed from the wash pump secondary outlet to a soil collector having a filter screen along the top portion. Wash liquid is sprayed from the wash arm through at least one jet toward the filter when the wash liquid is directed to the wash arm. A valve is provided for selectively deactivating wash liquid to the lower wash arm such that when the valve is open in a first position wash liquid flows to the wash arm and when the valve is closed in a second position wash liquid is prevented from flowing to the wash arm. The wash liquid can be diverted to an upper wash arm when the valve is in the second position. A pressure sensor senses soils in the soil collector. The pressure within the soil collector is monitored when the wash liquid is not directed through the wash arm to backwash the filter screen. If the pressure measurement exceeds a predetermined limit, a response is activated
For example, it is an object of the invention to provide a response of energizing a heater disposed in the sump region for increasing wash liquid temperature if the pressure sensor exceeds a predetermined limit.
It is a further object of the invention to provide a response of adding a wetting agent into the wash chamber.
It is an object of the invention to provide a response of adding detergent into the wash chamber.
Further, it is an object of the invention to provide a response of adding wash liquid to the wash chamber to help rinse soils away.
It is an object of the invention to provide a response of partial or complete draining of wash liquid from the wash chamber and the addition of fresh wash liquid if the pressure sensor exceeds a predetermined limit.
It is a further object of the invention to provide a dishwasher that operates with a cleaning cycle having a fill period and a wash period. The length of the wash period time can be increased if the pressure sensor exceeds a predetermined limit.